A device for controlling and isolating a tool in the form of an expansible sleeve for isolating areas in a well

ABSTRACT

The present invention relates to a device for controlling and isolating a tool for isolating areas in a well which comprises: a main inlet conduit which communicates with the inside of said casing, and which is obturated by a first element able to form a barrier to a fluid circulating in said casing, while yielding beyond a first pressure, this conduit communicating, with two auxiliary conduits, the ends of which join up in order to form an outlet conduit, one of these auxiliary conduits, forming a first chamber, while, in the other one, a second element is provided forming a barrier, moveable between a first position and a second position wherein said first position, said second element forming a barrier and the wall of said second auxiliary conduit make between them a sealed annular chamber in which prevails a so-called &lt;&lt;isolation&gt;&gt; pressure, this chamber not communicating with the outside, notably with the well.

The present invention relates to a device for controlling and isolating a tool in the form of an expansible sleeve for treating a well or a duct, this tool being connected to a casing for supplying a pressurized fluid and is inserted between said casing and the wall of said well or duct.

Expressed differently, it relates to a device at the bottom of a well, allowing isolation of the upstream space from the downstream space of an annular region comprised between a casing and the formation (i.e. the rock of the subsoil) or else between this same casing and the inner diameter of another casing already present in the well. This isolation has to be made while preserving the integrity of the whole of the casing (casing string) of the well, i.e. the steel column comprised between the formation and the well head.

It will be noted that a distinction has to be made between the integrity of the annular space and the integrity of the casing, both being essential for the integrity of the well.

The aforementioned annular space is generally sealed by using cement which in liquid form is pumped into the casing from the surface, and then injected into the annular space. After injection, the cement hardens and the annular space is sealed.

The cementation quality of this annular space is of very great importance for the integrity of the wells.

Indeed, this seal protects the casing from areas with salted waters which the subsoil contains, which may corrode them and damage them, causing possible loss of the well.

Moreover, this cementation protects the aquifers from the pollution which may be caused by close formations containing hydrocarbons.

This cementation forms a barrier protecting the risks of blowout caused by high pressure gases which may migrate into the annular space between the formation and the casing.

In practice, there exist many reasons which may result in an imperfect cementation process, such as the large well size, the horizontal areas thereof, difficult circulation or areas with loss. The result of this is a poor seal.

It will also be noted that the wells are increasingly deep, that most of them are drilled <<offshore>> at the vertical of water heights which may attain more than 2,000 m, and that the latest hydraulic fracturation technologies in which the pressures may attain more than 15,000 psi (1,000 bars), subject these sealed annular areas to very high stresses.

From the foregoing, it is clear that cementation of the annular space(s) is particularly important and any weakness in their making, while the pressures at play are very great (several hundreds of bars), may cause damages which may lead to the loss of the well and/or cause very substantial environmental damages.

The pressures in question may stem:

-   -   from the inside of the casing towards the outside, i.e. from the         inside of the well towards the annular space;     -   from the annular space towards the inside of the casing.

The casing (or casing string), the length of which may attain several thousand meters, consists of casing tubes, with a unit length comprised between 10 and 12 m, and assembled to each other through sealed threadings.

The nature and the thickness of the material making up the casing are calculated in order to withstand very great inner burst pressures or outer collapse pressures.

Further, the casing should be sealed during the whole lifetime of the well, i.e. for several tens of years. Any leak detection systematically leads to repairing or to abandoning the well.

The design, i.e. the configuration of the completion of the well should minimize the risks of communication between the inside and the outside of the casing. Also, the watch points are notably the following:

-   -   withstand the internal and external pressure stresses;     -   use steels compatible with the environment in order to avoid         risks of corrosion;     -   use screwed and sealed connection means;     -   avoid communications between the inside and the outside or, if         this is not the case, produce a seal with one or two barriers,         if possible by metal/metal contact.

Technical solutions are presently available in order to manage to make said annular space impervious.

Also, one of the techniques consists of positioning a deformable membrane around the casing at the desired location. The membrane is then deformed permanently, under the pressure of an inflating fluid, against the wall of the formation. As the membrane produces a seal on this wall, the annular space between the wall of the formation and the wall of the casing is then made impervious. This membrane may be in metal or elastomer, either reinforced or not with fibers.

Regardless of the type of membrane, the inflation of the latter requires the presence of a conduit for circulating the inflating fluid between the inside of the membrane and the inside of the casing. This circulation may be accomplished directly or via a system which may include from one to three valves according to the state of the art.

To the knowledge of the applicant, there exist 2 main possible configurations illustrated in the diagrams which are the subject of the appended FIGS. 1 and 3A.

According to a first technique illustrated in FIG. 1, a metal membrane 3 is positioned around a casing 2, pre-positioned in a well 1, and the inside of the membrane 3 is supplied with inflating fluid directly through a conduit 200 crossing the wall 20 of the casing 2.

If the pressure is increased inside the casing 2 until it attains a threshold giving the possibility of starting deformation of the metal membrane 3, the latter being directly connected to the casing 2, the membrane 3 deforms permanently. When the pressure decreases, the metal membrane retains its shape definitively.

A first drawback of this technique results from the fact that in the case of a failure of the metal membrane 3 leading to a loss of its imperviousness, direct communication between the annular space and the casing 2 is created.

A second drawback lies in the fact that in the case of multiple laying of membranes 3 as illustrated in FIGS. 2A and 2B, if the level of the hydrostatic pressure is identical in the casing 2 and in the annular space EA, then, when the pressure of the inflating fluid increases in the casing 2, the three membranes 3, distributed around the casing 2 and which may be separated by several hundred meters, are simultaneously deformed while inflation of the membranes one after the other from bottom to top, has more advantages, in particular with the view of ensuring the best possible cementation.

Individual inflation of each membrane 3 one after the other is not controllable in this configuration.

Further, after the laying, each membrane 3 continues to be subject to pressurization/depressurization cycles which might occur during the life of the well 1, embrittling the membranes 3, a little more at each cycle.

According to a second technique illustrated in FIG. 3A, the deformable membrane 3 consists of an elastomer either reinforced or not with fibers.

If this membrane 3 were directly connected to the casing 2 like in the previous case, it would deform elastically when the pressure in the casing 2 increases and it would regain a condition close to its initial shape as soon as the pressure decreases, by its elasticity.

It is therefore necessary to insert between the inside of the casing 2 and the inside of the membrane 3, a system of simple or multiple valve(s) 4 (illustrated here surrounded by an oval) giving the possibility of preserving and isolating the pressurized volume inside the elastomeric membrane 3 at the end of the inflating.

The pressure at the end of inflating is then determined by the closing of the isolation valve 4. Once this valve is closed, the membrane 3 can neither be emptied nor filled.

Further, in the case considered above of laying several membranes 3 on a same casing 2 at different depths or in order to avoid any inadvertent inflation, this system of multiple valves is provided in order to allow control of the beginning of the inflating of each membrane 3.

This system, for greater control, may even be completed by a frangible pin, called a <<knock-out plug>>, which opens the communication of the casing towards the control and isolation valves by breaking it, most often by having a ball circulate in the casing. But the insertion of the ball brings an additional constraint.

In order to produce these systems of multiple valves, analysis of the state of the art shows two different architectures: one uses sliding pistons, while the second uses sliding sleeves. In both cases, the pistons or sleeves are associated with breaking parts giving the possibility of controlling the opening or the closing of the pistons or sleeves, i.e. controlling the beginning and the end of the inflating of the inflatable membrane.

Such a system of valves is also advantageous in the case of a metal membrane in order to avoid inflating the membrane inadvertently and isolating it from changes in pressures of the casings, once it has been deformed.

Examples of such technologies equipped with filling valves are described in patents or patent applications US 2003/0183398, U.S. Pat. No. 4,260,164 and WO 2011/160193.

Such systems of metal or elastomer membranes, either reinforced or not, equipped with multiple valves, have several categories of drawbacks.

Firstly, these are drawbacks related to the expansible elastomeric membrane. Indeed, this membrane has time-limited strength and robustness. The isolation of the annular space between the upstream and downstream portions of the well cannot therefore be guaranteed in the long run.

Moreover, the loss of imperviousness of this membrane generates a weakened area with the inside of the well by removing a barrier.

Other drawbacks are related to the system of valves.

Thus, FIG. 3B is an enlargement of the system of valves 4 placed under the membrane 3 in FIG. 3A.

This system is a possible configuration typically consisting of two sliding valves 40 which may either be sliding pistons or sliding sleeves. These valves are placed in the conduit which puts the inside of the casing 2 in communication with the inside of the membrane 3.

Before inflating, one of the valves 40 is an obstacle to the inflating fluid. It is only possible to break this first barrier by increasing the pressure of the inflating fluid in the casing 2 beyond a certain pressure difference P1 predefined by a calibrated breaking element, the pressure difference occurring between the pressure of the casing and the pressure of the annular space. Once this difference P1 has been exceeded, the first barrier is broken and lets the inside of the casing 2 communicate with the inside of the membrane 3.

This breakage marks the beginning of the phase for inflating the membrane 3. The pressure is increased in the casing 2 in order to continue with inflating the membrane 3.

The end of the inflating is marked by the release of the movement of a second valve 40 in the casing-membrane communication conduit which will be an obstacle to the return of the pressurized fluid, in the direction from the membrane 3 to the casing 2. The movement of this valve is released by the breaking of a calibrated element, dimensioned so as to break as soon as the pressure difference between the membrane and the annular space exceeds a threshold P2 greater than P1. If the pressure further increases in the casing, the membrane 3 cannot be further inflated.

Further, once the inflating is finished, as soon as the pressure decreases, a return element brings the first valve 40 back to its initial position so as to form a second barrier in the communication conduit between the casing 2 and the membrane 3. Both valves are then in their final state as illustrated by FIG. 3B.

Thus, analysis of the prior art shows that all the devices for opening and closing the valves are activated by a pressure difference between the inside of the casing and the annular space comprised between the casing and the wall of the well.

Further, the seals of these valves 40 being subject to this casing/annular space pressure difference, whether they consist of a sliding piston or of sliding sleeves, are ensured by joints, noted as J in FIG. 3C and 3D, these joints being most often elastomeric joints.

When the breaking elements maintaining the valves 40 in place break, the sudden movements releasing the pistons or sleeves may damage these joints J. The seal at these valves is then no longer ensured, thereby creating direct communication between the casing 2 and the annular space EA (see FIG. 3C) or direct communication between the annular space EA and the membrane 3 (see FIG. 3D). In the latter case, if the membrane 3 is in an elastomer either reinforced or not with fibers, it deflates.

Moreover, no device gives the possibility of ensuring:

-   -   that the triggerings for opening and then for closing the valves         have actually been accomplished;     -   that the seal of the annular space between the upstream and         downstream portions of the well is effective over time.

Moreover, the stresses related to the integrity of the wells become increasingly large, whether this occurs at the level of the isolation:

-   -   of the annular space between the upstream and the downstream         portions of the well;     -   between the inside and the outside of the casing.

Preservation of the environment, public opinion, regulations, production of increasingly numerous wells for exploiting non-conventional resources forces this sector of technology to increasingly ensure that this seal is efficient, sustainable and controllable over several years.

The object of the present invention is precisely to propose a device which gives the possibility of avoiding this situation.

Thus, the present invention relates to a device for controlling and isolating a tool in the form of an expansible sleeve for treating a well or a duct, this tool being connected to a casing for supplying a pressurized fluid and is inserted between said casing and the wall of said well or of the duct, which comprises:

-   -   a main inlet conduit which communicates with the inside of said         casing, and which is obturated by a first element capable of         forming a barrier to a fluid circulating in said casing, while         yielding beyond a first predetermined pressure of said fluid,     -   this conduit communicating, downstream from said first element         forming a barrier, with two auxiliary conduits positioned in         parallel, the ends of which join up in order to form an outlet         conduit which opens into the inside of the pool,     -   one of these auxiliary conduits, said to be a <<first conduit>>,         notably forming with said first element, a first chamber in         which prevails an isolation pressure, while in the other,         called<<second conduit>>, a second element forming a barrier is         provided, moveable between a first position in which it         obturates the second conduit while leaving clear communication         between the first conduit and the outlet conduit, and a second         position in which it prevents any communication between the         auxiliary conduit and the outlet conduit, the passing from one         position to the other being accomplished by the breaking of a         pin under the effect of the increase in the pressure of the         fluid up to a second predetermined pressure, greater than said         first pressure, characterized by the fact that in said first         position, said second element forming a barrier and the wall of         said second auxiliary conduit make between them a sealed annular         chamber wherein a so-called<<isolation pressure>> also prevails,         this chamber not communicating with the outside, notably with         the well.

According to other non-limiting and advantageous features of the invention:

-   -   said second element comprises a piston constantly urged towards         said second position;     -   said second element includes a frangible part, such as a pin,         positioned in the sealed chamber and which yields when the         second predetermined pressure is attained;     -   said isolation pressure is equal to atmospheric pressure or is         slightly greater;     -   said second element includes a metal<<nose>> which, in said         second position, is in contact and provides a seal with the wall         of the outlet conduit, also in metal;     -   an anti-return valve is positioned inside the outlet conduit;     -   the seal of said valve is ensured by a metal/metal contact;     -   said expansible sleeve is in metal;     -   the device includes means for acoustically recording the         breaking of the elements forming a barrier and means for         recording the pressure in the annular space;     -   said recording means may be remotely polled via an RFID         technology.

Other features and advantages of the invention will become apparent upon reading the detailed description which follows. In addition to

FIGS. 1 to 3D on which comments have already been made above, reference will be made to the appended drawings wherein:

FIGS. 4A and 6B are simplified views, in a longitudinal sectional view, of a well portion equipped with a casing with an expansible sleeve and with the device according to the invention; and

FIGS. 4B, 5 and 6A are more detailed, enlarged longitudinal sectional views of an embodiment of the device;

FIGS. 7A and 7B are sectional views similar to those of

FIGS. 4A and 6B further illustrating detection means;

FIGS. 8A to 8D show in a longitudinal sectional view, a well portion, the casing of which is equipped with several sleeves.

FIG. 4A illustrates a sectional view of a casing 2 positioned in the well 1 before cementation.

This casing is equipped with a deformable membrane 3 in metal which is provided with the control and isolation device illustrated here surrounded by an oval. A case allowing the recording of the breakages of the elements of the control device forming a barrier on the one hand and of a pressure of the annular space placed above the metal membrane, i.e. inserted between this membrane and the surface, on the other hand.

The control and isolation device includes a conduit C, this conduit including a burst disc and two anti-return valves V1 and V2, one of which is equipped with a frangible element F. The space between the burst disc and the valve V1 delimiting a chamber CH1 is at a pressure substantially equal to atmospheric pressure, and the device also includes a second isolated chamber CH2 at a pressure substantially equal to atmospheric pressure.

The disc, the valves V1 and V2, the element F are not illustrated in FIG. 4A: these elements will be described in more detail hereafter, notably with reference to FIG. 4B, including an enlargement of the control and isolation device.

As already stated above, the device comprises a main inlet conduit C which communicates with the inside of the casing 2 via a drilled hole 200 opening into the wall 20 of the casing. The conduit C is obturated by a first disc-shaped element 5, for example in metal, which is able to form a barrier to a fluid circulating in the casing, while yielding beyond a first predetermined fluid pressure P1.

This conduit C opens into a chamber 60, the cylindrical wall of which is referenced as 600.

Via this chamber, the conduit C communicates with two auxiliary conduits 6 and 8 positioned in parallel, the end of which join up in order to form an outlet conduit 9 which opens into the inside of the tool 3.

One of these auxiliary conduits, a so-called<<first conduit>> 8, includes an inlet 80 and an outlet 81 which extends perpendicularly to the axis of the casing.

The inlet 80 opens into the chamber 60, while the outlet 81 slightly opens upstream from the two anti-return valves when they are in the closed position.

This first auxiliary conduit 8 forms a first chamber. The chamber 60 is part of the second auxiliary conduit 6 and has, from upstream to downstream, i.e. from left to right, when FIG. 4B and the fluid flow direction, a first cylindrical segment 61 with a wall 610, of a small diameter, an intermediate segment 62 of larger diameter and with a wall 620, an intermediate region of which 630 has a diameter slightly larger, are considered. As this will be seen later on, this wall contributes to delimiting a second chamber CH2.

The segment 62 substantially continues with the same diameter as its inlet, but includes a section restriction which makes it join the outlet conduit 9. Inside the conduit 6, an anti-return valve V1 is positioned, which consists of a piston 7 having an elongated body 71.

In its upstream portion, it includes a head 70 having a longitudinal recess 700 in which a coil spring R extends. This spring is supported on the upstream end of the segment 62 and tends to push the piston from upstream to downstream.

The head 70 is peripherally provided with a joint J, which ensures a perfect seal between the piston and the segment 62 of the conduit 6.

Downstream from the recess 700, the body 7 is crossed right through by a frangible element or pin F which, as this will be seen later on, is intended to break under the effect of a pressure P2 greater than P1. For this purpose, it has regions of lower strength.

In its downstream portion, the piston continues with a nose 72, the diameter of which is substantially equal to that of the corresponding segment of the conduit 6. It is also provided with a seal gasket J similar to the previous one, and with a truncated end surface 720, the function of which will be explained later on.

The outlet conduit 9 from downstream to upstream has a segment 90 with a wall 900, which opens inside a conduit of smaller diameter 91, and with a wall 910 in which a coil spring is positioned. This spring bears against a bead B which forms an anti-return valve obturating a segment 92 with a still smaller diameter, which itself communicates with the conduits 6 and 8.

A frustroconical transition area 930 makes the upstream end of the outlet conduit 9 communicate with the auxiliary conduit 6.

We shall now explain the operation of the device according to the invention.

FIG. 4B illustrates a preliminary situation in which the device has not yet been lowered into the well.

Before lowering it into the well, water is circulated in the casing 2 so that the inside of the inflatable membrane 3 is filled with water, this for avoiding its collapse by the increase in pressure of the well during its lowering.

Of course, to do this, the burst disc 5 is not yet installed and the water may then cover the inlet conduit C, the auxiliary conduit 8 and then the outlet conduit 9 by pushing the bead B against the spring R.

During this phase, the chamber CH2 delimited by the segment 63 of the conduit 6 and the piston 7 is at atmospheric pressure and does not fill with water. It will indeed be noted that at this stage, any passing of fluid into the conduit 6 is impossible since the piston 7 is immobilized by the frangible pin F, and the piston plus pin assembly being maintained in position by a return spring R.

In order to close the assembly with the burst disc 5, a portion of the water, circulating in the chamber CH1 delimited by the conduit 8 and the segments 80, 81, 60, 61, 62 and 92, is purged so that the filling of this chamber is for a major part ensured by air at atmospheric pressure.

Once the assembly is in place in the well 1, the pressure inside the casing 2 increases and becomes clearly greater than atmospheric pressure.

As long as the pressure difference between the casing 2 and atmospheric pressure in the chamber CH1 remains below the pressure P1 for breaking the disc 5, the assembly of the device remains closed and the deformable membrane 3 cannot inflate.

In order to inflate this membrane, the pressure again needs to be increased inside the casing 2 from the surface by pumping until the pressure difference is sufficient for breaking the disc 5. The predetermined pressure P1 has then been attained, which is the pressure for breaking the disc.

Under these conditions, the conduit portion 62 is filled with liquid but the valve V1 is always blocked by the presence of the frangible finger F.

On the other hand, the fluid flows through the conduit 8 as well as through the valve V2, since the fluid pressure is sufficient for pushing back the bead B against the spring R.

The breaking of the disc 5 corresponds to the beginning of the inflating of the membrane 3. This breaking may be acoustically detected and recorded by a case provided for this purpose and positioned close to the surroundings of the membrane.

The situation of FIG. 5 is then again found, wherein, except for the chamber CH2 which remains at a pressure substantially equal to atmospheric pressure since it is isolated with two joints J, the remainder of the conduits is at the inflating pressure.

The pressure is then increased until the pin F is broken, which corresponds to the position of FIG. 6A. A predetermined pressure P2 for breaking the calibrated pin has then been attained, the pressure P2 being greater than the pressure P1. Consequently, the pin no longer opposes the movement of the piston 7, which is released and pushed back from upstream to downstream under the effect of the return spring R.

However, this sliding is limited since the nose 72 of the piston 7 comes into contact with the inlet of the outlet conduit 9 by metal/metal contact of the frustroconical surfaces 720 and 930.

In this way, the membrane 3 can no longer be inflated. It cannot either be deflated because of the presence of the valve V2 since the bead B bears against its seat.

Subsequently, when the pressure of the casing is purged and the latter returns to its hydrostatic pressure level, the whole of the conduits upstream from the valve V2 returns to the pressure of the casing.

If the pressure inside the casing were to increase again, for example in order to inflate another membrane, the valve V1 would remain in the closed position and therefore the membrane 3 would remain also completely isolated.

Thus, the end of the expansion is marked by the breakage of the pin which gives the possibility of closing the access path in the direction from the casing to the deformable membrane, while releasing the movement of an anti-return valve. This valve is maintained in its closed position by means of a spring. When the pin is broken, the valve moves and sets the chamber initially at atmospheric pressure to the pressure of the casing. Both joints J then no longer have any function.

The breakage of the pin may be acoustically detected and recorded by a case provided for this purpose and positioned in the surroundings of the membrane.

At the end of the inflating, the membrane remains at its inflating pressure and for each valve, the seal is guaranteed by a metal/metal contact.

This situation is illustrated by FIG. 6B which illustrates a schematic diagram of the membrane+control and isolation device assembly after inflating the membrane.

The conduit C now includes 2 anti-return valves which are opposed to each other, the chamber, initially at atmospheric pressure, is now at the pressure of the casing and is no longer of any use.

In FIG. 7A, the case BO giving the possibility of recording the breakages of the elements of the barrier-forming control device on the one hand and the long term changes in the pressures of the annular space EA on the other hand, is placed above the metal membrane, i.e. inserted between this membrane 3 and the surface or between two membranes 3.

In the case of multiple laying of membranes 3 for a same casing 2, each membrane will be equipped with a case BO placed as close as possible to the membrane 3 with which it is associated. Each case BO then allows detection and recording of the breakages of the disc 5 and of the pin F, the breaking of the disc indicating that the pressurized filling of the membrane has properly taken place, while the breaking of the pin indicates that the inflating was finished and that the membrane is isolated.

The case also allows recording of possible pressure variations in the annular space for several years after laying the membrane.

For this purpose, the case BO is advantageously placed above the membrane 3 since it gives the possibility for example, in the case of imperfect cementation under the membrane leading to a loss of the seal of the cement along the wall of the formation, of checking whether the metal membrane 3 has ensured its role by sealing the annular space EA situated between the membrane 3 and the surface of the well 1.

The case BO, if it records the pressure variations of the annular space, therefore has a risk of possible communication between the inside of the case and the annular space EA. Still, for the sake of ensuring the integrity of the casing 2 relatively to the annular space EA, the case BO is therefore detached from the membrane 3 and from the control device. The disc 5 and pin F breakages are acoustically detected remotely by the case BO placed at a few tens of centimeters.

According to FIG. 7B, as the case BO is able to be queried over a short distance by using RFID technology, the querying of the case BO and the recovery of the data may be accomplished in the well 1 before or after laying the membrane 3 by using a tool A provided for this purpose and connected from the surface through a<<wireline>> cable for example.

The advantages related to the creation of a reference pressure chamber for triggering the breakage of weak points at atmospheric pressure are the following: the reference pressure is not the pressure of the well, so that a conduit has been removed between the inside of the casing 2 and the annular space of the well 1.

Moreover, any risk of leaks between the inside of the facing 2 and this annular space EA is suppressed at this control device.

Further, upon opening the access valve between the inside of the casing and the inside of the expansible structure, the opening pressure is exclusively related to the pressure in the casing.

According to FIGS. 8A, 8B, 8C and 8D, if in the well there exist several devices of this kind, because of the hydrostatic pressure which increases with the depth and since the reference pressure is substantially equal to atmospheric pressure, they will naturally open from bottom to top, which will avoid generations of traps for the fluid.

The advantages related to the creation of a valve with a metal-on-metal seal associated with an anti-return bead essentially lie in the fact that this seal is made without using elastomeric gaskets, whence better durability over time.

Moreover, the seal is proportional to the applied pressure, and the more the pressure increases, the more the seal is efficient.

The use of a metal disc 5 makes it long-lasting over time and makes it have a very high imperviousness level.

Finally, the advantages related to the setting into place of an electronic system for recordings and measurements via RFID are of being informed on the proper execution of the opening and closing process of the inflating valve, and of a possible measurement over time of the pressure in the annular space. 

1. A device for controlling and isolating a tool in the form of an expansible sleeve for treating a well or a duct, this tool being connected to a casing for supplying a pressurized fluid and is inserted between said casing and the wall of said well or of the duct, which comprises: a main inlet conduit which communicates with the inside of said casing, and which is obturated by a first element able to form a barrier to a fluid circulating in said casing, while yielding beyond a first predetermined pressure of said fluid, this conduit communicating, downstream from said element forming a barrier, with two auxiliary conduits positioned in parallel, the ends of which join up in order to form an outlet conduit which opens inside the tool, one of the auxiliary conduits, called<<first conduit>> forming, notably with said first element, a first chamber in which prevails an isolation pressure, while in the other one, called <<second conduit>>, a second element is provided, forming a barrier moveable between a first position in which it obturates this second conduit while clearing the communication between the first conduit and the outlet conduit, and a second position in which it prevents any communication between the auxiliary conduits and the outlet conduit, the passing from one position to the other being accomplished by increasing the fluid pressure to a second predetermined pressure greater than said first pressure, wherein in said first position, said second element forming a barrier and the wall of said second auxiliary conduit make between them a sealed annular chamber wherein a so-called <<isolation>> pressure also prevails, this chamber not communicating with the outside, notably with the well.
 2. The device according to claim 1, wherein said second element comprises a piston constantly urged towards said second position.
 3. The device according to claim 1, wherein said second element includes a frangible part, such as a pin, positioned in the sealed chamber and which yields when the second predetermined pressure is attained.
 4. The device according to claim 1, wherein said isolation pressure is equal to atmospheric pressure or is slightly greater.
 5. The device according to claim 1, wherein said second element includes a metal <<nose>> which, in said second position, is in contact with the wall of the outlet conduit, also in metal, the assembly thereby forming a metal/metal seal.
 6. The device according to claim 1, wherein an anti-return valve is positioned inside the outlet conduit.
 7. The device according to claim 6, wherein the seal of said valve is ensured by a metal/metal contact.
 8. The device according to claim 1, wherein said expansible sleeve is in metal.
 9. The device according to claim 3, wherein it includes means for acoustically recording the breakage of the barrier-forming elements and means for recording the pressure in the annular space.
 10. The device according to claim 9, wherein said recording means may be queried remotely via RFID technology. 